1. Field of the Invention
The present invention relates to a power transmission mechanism having a dog clutch.
2. Description of the Related Art
As an example of a power transmission mechanism having a dog clutch, as disclosed in Japanese Unexamined Patent Publication No. 10-61731, there is a gear-type transmission mechanism for vehicle mounted on a motorcycle. As is well known, the gear-type transmission mechanism has a plurality of rotational shafts such as an input shaft for changing and an output shaft for changing. An input-side gear (rotor) for changing is fitted to the input shaft. An output-side gear (rotor) engaging with the input-side gear is fitted to the output shaft. For the shift operation, an appropriate gear for changing is spline fitted to the rotational shaft so as to be slidable in an axial direction, and a dog clutch is interposed between the slide-type gear and a play-type gear for changing that is rotatable relative to the rotational shaft and is engaged so as not to be moved in the axial direction. The dog clutch connects and disconnects (disconnectably connects) power transmission between the gears.
FIG. 10 illustrates a conventional dog clutch arranged between gears on an output shaft for changing of a gear-type transmission mechanism. In FIG. 10, an appropriate slide-type gear for changing 105 is spline fitted to an outer peripheral surface of an output shaft 100 so as to be slidable in an axial direction. A play-type gear for changing 106 is rotatably fitted to the output shaft 100 via a bearing member 109 and is engaged by an engaging ring 107 or the like in an axial direction. A dog clutch C0 for disconnecting power transmission between the gears 105 and 106 is interposed between the gears 105 and 106.
The dog clutch C0 has a plurality of the dog jaws 111 and a plurality of engaging holes (recess portions) 112. The dog jaws 111 are formed in a ring body 110 integrally formed with the slide-type gear 105 at equal spaces in a circumferential direction and are protruded toward the play-type gear 106 in an axial direction. The engaging holes 112 of the same number as that of the dog jaws 111 or of the number of an integral multiple of the dog jaws 111 are formed in an arm wall 113 of the play-type gear 106. A shift fork 121 moved by a change drum (not shown) in an axial direction of the shift fork supporting shaft (not shown) engages in an annular groove 120 of the slide-type gear 105. The slide-type gear 105 is moved by the shift fork 121 toward the play-type gear 106 in the axial direction of the output shaft 100 (in a direction of an arrow F1) to engage each of the dog jaws 111 in each of the engaging holes 112 for connecting the gears 105 and 106 so as to transmit power. In such a conventional dog clutch C0, an end face 111a of the each dog jaw 111 in the axial direction and a wall surface 113a of the play-type gear 106 on the slide-type gear 105 side are formed in a planar shape substantially perpendicular to an output axis O.
When the dog clutch C0 of FIG. 10 is connected, as described above, the slide-type gear 105 is moved in the direction of the arrow F1 to fit each of the dog jaw 111 into each of the engaging hole 112 for engagement. In the moving process, each of the dog jaw 111 may be directly fitted into each of the engaging hole 112 without being abutted on the wall surface 113a. However, in more than half the number of shift operations, the end face 111a of the dog jaw 111 is once abutted on the wall surface 113a. Thereafter, by the relative rotating between the gears 105 and 106 in a circumferential direction, each of the dog jaws 111 is fitted into each of the engaging holes 112 and is then moved in the direction of the arrow F1 so as to be brought into a complete clutch connection state. That is, when the abutment of the dog jaw 111 occurs while the slide-type gear 105 is moved, the rotation of the change drum and the movement of the slide-type gear 105 will be once stopped.
However, when the dog jaw 111 is abutted on the wall surface 113a, misalignment corresponding to a gap in the radial direction between an inner peripheral spline of the slide-type gear 105 and an outer peripheral spline 101 of the output shaft 100 occurs in the slide-type gear 105 and the slide-type gear 105 is slightly inclined. Thereby, the sliding resistance of the spline fitted portion is increased due to the misalignment and inclination. Moreover, when the dog jaw 111 is fitted into the engaging hole 112 and the dog jaw 111 and the edge of the engaging hole 112 in a circumferential direction are pressed into contact with each other, the sliding resistance is increased. Due to the increase in the sliding resistance, the dog jaw 111 can be stopped before the clutch is completely connected. Thus, half-engagement and jump out of gear can occur, and moreover, the shift operation becomes heavy.
FIG. 9 illustrates a variation of the rotational angle of the change drum with time in an absence of the abutment of the dog jaw (an imaginary line graph X1) and a variation of the rotational angle of the change drum with time when half-engagement occurs through the abutment of the dog jaw (a solid line graph X2).
The graph X1 is an example in which the change drum is rotated without being stopped, from a second gear position (+30°) indicated by a reference numeral P1 to a third gear position indicated by a reference numeral P2 in the absence of the abutment of the dog jaw. In a case where the clutch is connected through the abutment state of the dog jaw, as illustrated in the graph X2, when the dog jaw is abutted at a position P3 (around −15°) during shifting, the gears are shifted relatively in a circumferential direction so that the dog jaw is fitted into the engaging hole. The sliding resistance of the splined portion due to the misalignment is increased, and the change drum is stopped at a position P4 before a third gear position P5. Thereby, half-engagement is continued for a fixed period of time T1.